CUMBERLAND ISLAND — Drops of moisture fall from the Spanish moss that hangs from live oaks onto the fan-shaped palmetto fronds below. A hungry armadillo busily scavenges under vines and ferns. A breeze off the teal Atlantic plays with the mane of a sturdy feral horse trotting on the ivory sand dunes.To land on Cumberland Island, a national seashore off the Georgia coast, is to immerse oneself in the sounds of silence just a few miles east of one of the nation’s busiest interstate highways, I-95.The southernmost of Georgia’s barrier islands, it is accessible only via ferry — frequently escorted by dolphins and pelicans — and the private launch of the island’s only deluxe inn.